What immunohistochemical findings are observed in the diagnosis of a Merkel cell carcinoma (MCC) tumor?

Updated: Jan 18, 2019
  • Author: Arjun S Joshi, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Definitive diagnosis is based on the presence of antibodies to cytokeratin (CK) 20 (in the form of a perinuclear dotlike pattern typical of neuroendocrine tumors), neuron-specific enolase, synaptophysin, and chromogranin. CK19 expression is increased in tumors positive for the Merkel cell polyomavirus and may help in diagnosis of CK20-negative tumors. [16]

The absence of S-100 protein and homatropine methylbromide marker essentially excludes the diagnosis of malignant melanoma. Likewise, the absence of leukocyte common antigen excludes cutaneous lymphoma.

Epithelial membrane antigen and BEP-EP4 can also be found in MCC.

Cytokeratin 7 is found in bronchial small cell carcinoma and not in MCC.

MCC tumors infected with the Merkel cell polyomavirus (MCV) characteristically show immunoreactivity with monoclonal antibodies against the MCV large T (LT) antigen [11] in up to 97% of cases. [17]

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